1. Field of the Invention
This invention pertains to an improved electronic circuit to start and light a fluorescent lamp utilizing a SCR starter and inductive coupling for stable high frequency square wave input into the lamp. The electronic circuit described herein is capable of starting fluorescent lamps of different sizes and makes.
2. Description of the Prior Art
In the prior art, basic electric circuits for operation of fluorescent lamps include preheat, instant-start and rapid-start circuits. Each includes a ballast, which provides starting voltage, and limits current.
In preheat circuit, a starting switch, usually an automatic starter is used to heat the electrodes. The most common starter employs a tiny argon glow tube with one fixed electrode and one electrode made of a bent bimetallic strip. In the instant-start circuit, the ballast voltage is much higher than in the preheat circuit. The rapid-start ballast has transformer windings that continiously provide the desired voltage and current for electrode heating to release enough electrons to arc from the voltage of the main windings. The combination of heat and moderately high voltage permits quick lamp starting with smaller ballasts than those for instant-start lamps, reduces flicker associated with preheat lamps.
These circuits are essentially low frequency, that is same as line frequency sine wave power supplies, with the disadvantages of flicker, audible hum and fractional use of sine wave voltage for light generation as shown in FIG. 1a, with considerable idle time of t.sub.1 to t.sub.2 as indicated, and consequently less efficient with annoying flicker. These circuits use bulky transformers, capacitors and inductors for proper start and stabilization of the arc discharge, and thereby they are associated with the problem of more power losses associated with copper and iron. These circuits also give rise to considerable polarization at electrodes of the lamp due to low frequency alternating voltages, which result in low life, reduced light output and degraded performance of the lamp. Furthermore, these circuits are not universal, that is, they can not handle defferent sizes and shapes of lamps, because of close matching requirements of reactances at low frequencies.
High frequency circuits have been known in the prior art, designed to avoid some of the aforecited disadvantages inherent with low frequency circuits. They operate on a.c. circuits with 50 to 60 Hz input and 360 to 3,000 Hz output, and uses various types of frequency converters to obtain high frequency power. (Refer: R. D. Burham, "High-frequency Lighting", Architectural Record, Dec., 1957). Motor generator sets are most common, but static magnetic converters and converters using transistors have been developed. (Refer: J. H. Campbell & E. G. Downie, "Magnetic Frequency Multipliers For High Frequency Operation of Fluorescent Lamps", Electrical Construction And Maintenance, Nov. 1954, p. 89. and "Transistorized High-frequency Systems Developed for Lighting", Architectural Record, Jan., 1958).
The high frequency circuits available for fluorescent lamps, in the prior art, are complex and expensive. They are less efficient and less reliable. Furthermore, they are not universal, i.e., each type of fluorescent lamp requires its own matched circuit. Therefore they are not popular.